Study of gigantic third-order optical nonlinearity in low-dimensional correlated electron systems

点击翻译按钮获取中文摘要

The purpose of this research project is to measure quantitatively third-order nonlinear susceptibility χ^<(3)> spectra and clarify the mechanism of third-order optical nonlinearity in one-dimensional (1D) correlated electron systems of halogen-bridged nickel compounds and 1D and 2D cuprates. We have performed several kinds of nonlinear spectroscopy measurements on these materials such as -scan measurements and transimission-and reflection-type third harmonic generation (THG) measurements. The main results are as followed.○ In the 1D cuprates and the nickel compounds, odd and even excited states are degenerate. In the 2D cupreates, on the other hand, the even excited state locates at the energy slightly lower than the odd excited state. Such a difference between the 1D and 2D cuprates is related to the fact that charge and spin degrees of freedom are separated in the 1D system, but coupled in the 2D system. In the 1D system, therefore, the transition dipole moments between the ground state and the odd excited state and between the odd and even excited states are enhanced and then the larger χ^<(3)> is obtained○The magnitude of χ^<(3)> of the bromine-bridged nickel compound evaluated by the reflection-type THG measurements is extremely large, exceeding 10^<-8> esu. In this compound, the relaxation of the photoexcited state is very fast, and the spectral width of the absorption is very small, suggesting its high potential as a good nonlinear optical material for applications.